Current surface-mounted devices of light-emitting diodes (SMD LED) fail to emit most of the light because of the difference in the refractive index of the epoxy resin and the atmosphere during the packaging process (The nair refractive index of the atmosphere is 1, and the nepoxy refractive index of the epoxy resin is around 1.5). This is evidential as follows:
For a plane surface of the component, the Snell""s Law shows:
n sin(xcex8)=xe2x80x2 sin(xcex8)
then
nair sin(xcex8air)=nepoxy sin(xcex8epoxy); nair=1 (as shown in FIG. 1)
sin(xcex8air)=1.5xc3x97sin(xcex8epoxy)
In this example, the maximum angle xcex8air of the light injected from the epoxy resin to the atmosphere is 90xc2x0. The calculating formula states as follows:
Sin(90xc2x0)=1.5xc3x97sin(xcex8epoxy)
xcex8epoxy=sinxe2x88x921(1/1.5)=0.729728=0.728728xc3x97180/xcfx80=41.8xc2x0
Here, 41.8xc2x0 stands for the critical angle. In other words, a LED light-emitting chip emits 180xc2x0 of light, yet only 41.8xc2x0xc3x972=83.6xc2x0 of the light is injected directly from the component. Other light has to be injected (or might even be blocked completely from injecting) after several times of refraction and a loss of brightness, which reduces the efficiency of the brightness (as shown in FIG. 2).
Present SMD LED is subjected to the molding technology and the cost. The appearance of traditional epoxy resin is no more than plane convex and a compound of both as shown in FIGS. 3, 4 and 5. A single convex surface increases the volume of the product, despite of its improvement in the brightness of the light. The most serious disadvantage is that during the pick and place operation of the LED component, the vacuum extractor tends to leak out the air due to the convex surface of the component, which causes insufficient vacuum, loss of the material during operation and slants of the location. In sum, the disadvantages of traditional SMD LED mentioned above include:
1. Low brightness effect
2. The convex surface of the encapsulating resin of SMD LED enhances the brightness; however, the design increases the volume of the component.
3. The convex component of SMD LED causes a loss of material during the pick and place operation, which even causes the machine to break down.
4. The convex component of SMD LED causes displacement during the pick and place operation and brings more trouble to the operation.
The surface-mounted devices of light-emitting diodes with small lens for the present invention uses dedicated molding. Each lens possesses a diameter between 10 um to 200 um, which is hard to make by traditional machines. Such molding that forms small lens makes use of Lithographice Galvanoformung and Abformung (LIGA) that develops the image by the exposing of the resist and then shapes the remained photoresist into spherical surface by heating. After being plated with metal conducting layer, the SMD LED with small lens are molded.
The molding by Lithographice Galvanoformung and Abformung transcends traditional molding machines and manufactures molds with small lens that traditional machine and processing technology could never achieves, so as to apply them to the packaging (such as: molding). In this way, small lens can be equipped on the surface of SMD LED.
The surface of SMD LED attached with small lens enhances the critical angle of the light emitted from the light-emitting chip (dice). Therefore, by collecting the light from the light-emitting chip (dice), the brightness is enhanced and the direction of the light becomes more centralized.
By designing the small lens into diffraction lens that provides diffraction function to focus the light, the light on each spot of the packing resin (Epoxy) is focused on the focus after passing through the diffraction lens, which in turn achieve the goal of increasing brightness.
Meanwhile, since the surface of SMD LED appears to be plane under the vision of naked eyes, the user doesn""t have to worry about the insufficiency of vacuum caused by the vacuum extractor""s leaking air during the pick and place operation that might lead to a loss of materials and displacement during the operation, and brings trouble to the follow-up replenishment and operation.
The SMD LED with small lens possess the following advantages:
1. Conserve each advantage of the SMD LED
2. Increase the brightness of LED. Centralize the direction of the light.
3. Prevent the volume of the component from increasing during the process of increasing the brightness.
4. Keep the vision on the plane surface. Improve the efficiency and quality during the fixing operation of the component.
Following is the illustrative diagram and description of the surface-mounted devices of light-emitting diodes for the present invention.